1. Field of the Invention
The present invention relates to a system for inspecting large-volume goods, in particular freight goods, with an x-ray source, which emits x-rays for irradiating the goods, and with a detector arrangement aligned with the x-ray source.
2. Description of the Background Art
As is generally known, x-ray systems, which have an x-ray source and a detector arrangement aligned with the x-ray source, are employed to inspect large-volume freight goods such as truck or container loads. While the goods to be inspected are moved between the x-ray source and the detector arrangement relative to these, they are irradiated by x-rays and scanned in addition. For the relative movement between the inspection system and the inspection goods, either the inspection goods themselves, for example, a truck, move between the x-ray source and the detector arrangement, or the inspection system has its own drive by which it is moved relative to the inspection goods.
To inspect the inspection goods in a scanning process, it is known to arrange the detectors in the detector arrangement in corresponding detector rows. As described in DE 101 22 279 A, which corresponds to U.S. Pat. No. 7,308,076, and which is incorporated herein by reference, the detector arrangement contains two detector rows at right angles to one another, one of which extends vertically upwards and the other horizontally above the inspection track.
Cargo scanning systems use mainly cesium iodide (CsI) scintillators for detecting transmitted x-rays. Ceramic scintillators are employed in part in baggage inspection systems. This has not been the case so far in freight scanning systems, because due to the large inspection surface and the huge number of required crystals the cost of the detectors would represent too great a share of the manufacturing costs.
High energy x-rays of, for example, 3.5 to 4 MeV are used to penetrate trucks and containers. The x-rays are generated by pulsed electron accelerators. Detectors with a specific depth are needed because of the high energies. The depth is measured here in the direction of the x-ray source and thereby perpendicular to the direction of movement of the inspection goods.
At higher relative speeds of the inspection goods it is difficult to generate good images without stripes, because to accomplish this the relative speed must be matched to the pulse rate dependent on detector dimensions.
In freight inspection systems, an increasingly better image resolution and a higher penetration are required. These can be achieved by improvements in the x-ray source and the detectors.